i Field of the Invention
This invention relates to a composition comprising a homogeneous, viscous continuous phase and a discontinuous phase of hollow, organic polymer microspheres; the invention also relates to a buoyant putty of such composition in which sinkable objects can be wrapped or embedded to keep them afloat, for example if accidentally dropped overboard from a boat, and for other applications.
ii Description of Prior Art
Through being denser than the medium in which they have been immersed, many objects that would otherwise endure at least a brief wetting, are often irretrievably lost upon accidental release into deep, clouded or cluttered water, through sinking. Such accidental release may occur during the course of recreational or commercial activities; from a ship, boat, dock, shore, or the body of a wader or swimmer; into a pond, pool, canal, swamp, river, lake or ocean; objects commonly lost in such fashion include glasses, pens, watches, combs, coins, cards, keys, tools, instruments, utensils, jewelry, as well as rods, lures, hooks and other fishing accessories, that contain substantial quantities of metal, glass, ceramic, stone, bone, or most kinds of fibers, rubbers, resins or plastics, or even certain woods such as ebony.
Such losses are always annoying and often costly. It is often not practical, convenient or comfortable to keep such sinkable objects held or tied to a person, boat or shore at all times, nor to permanently incorporate low-density parts or materials into their design for the sole purpose of keeping them afloat in the event of accidental release. Certain buoys or other flotation devices exist of a shape or with accessories that allow them to be temporarily tied or fitted to particular types of sinkable objects during the use of these near water, to be later detached for easier transport or storage. One example of these is the "Aqua Float Rod Floater", from Marine Manufacturing Industries (M.M.I.) Inc., Ile des Soeurs (Montreal), PQ Canada, a "tubular split foam device that fits around a fishing rod between the handle and the first eyelet" (Marine Manufacturing Industries Inc., "Aqua Float: The Fisherman's Friend" (pamphlet), Montreal, PQ, Canada, 1995). Such devices, whether made of wood, plastic or other solid materials, that often contain either one or a few large enclosed spaces, or many small closed cells, that are filled with air or inert gas to reduce overall density, are often of size or shape unsuitable for use with other than a limited variety of sinkable objects. Even pieces of soft closed cellular foams, composed of elastic flexible material that imprisons numerous air bubbles in a permanent arrangement, for example some types of foam rubber or polyurethane, that can be wrapped around sinkable objects of various shapes, will tend to revert to non-wrapping shapes in an elastic manner unless restrained by ties, adhesives or envelopes. Also, though either rigid or soft foams can be cut to accomodate smaller sinkable objects, they cannot thereafter easily be re-joined for use with larger ones.
A better way to protect sinkable objects would use a material that is a putty of lowest possible density that can be inelastically deformed to a new stable shape that surrounds or otherwise holds a sinkable object without need for ties, adhesives or envelopes. Only a sufficient quantity of buoyant putty to float a smaller sinkable object need be detached from a larger mass; or, several such small quantities could be joined to be able to float a larger sinkable object, or to be stored or transported as a larger mass.
The lowest density that can be achieved with a homogeneous organic material that can be inelastically deformed, for example, unvulcanized rubber, oligoisobutylene or similar flowable hydrocarbon, is about 0.910 g/mL. Since this density is not much less than that of water, fresh water having a density of 1 g/mL, relatively large quantities of such material would be necessary to float most sinkable objects. To enable the greater buoyancy that would be necessary for practical applications, substantial quantities of air or other gas would therefore need to be incorporated, for the lowest possible overall density. However, a material that would be capable of inelastic deformation through flow would not be able to retain loose air bubbles, each of which would eventually break and release its air on contact with the outside surface, or merge on contact with other bubbles to form larger and still unstable voids, thus causing phase-separation within the mass, and even breaking it up to release a held sinkable object. Also, a flowable material that is homogeneous, even if buoyant, would continue to flow under even very mild forces, and thus would not be able to sufficiently retain a shape that could hold a sinkable object in the manner of a putty.
Surrounding each of many tiny air bubbles in its own light plastic membrane would allow them all to be retained, evenly dispersed, within the mass of a highly viscous fluid, yet allow them to slide past each other as a portion of the material is inelastically deformed to a new shape. Such a material would now be highly buoyant; moreover, it would have the desirable consistency and flow properties of a putty, by analogy with other heterogeneous composite mixtures that are putties.
A putty is generally formulated as a simple composite material that usually consists of a collection of discrete particles, such as powdered calcium carbonate as the discontinuous phase, suspended in a viscous liquid, such as oil as the continuous phase. A certain minimum force is required to overcome the static friction between the particles; below this critical force the material tends to retain the shape given it. This mechanical property has allowed "putties" or "caulks" to be used for centuries to seal small cracks in boats or housing, by forming a plug within a hole that, in contrast with flowable homogeneous materials, does not continue to flow out under gravity or water pressure. In general, the volume of viscous liquid in a putty must be sufficient to fill the voids between the particles, but not so much as to allow the particles to settle and the liquid to exude for the whole material to phase-separate. In the case of approximately spherical particles, the volume-to-volume ratio of continuous to discontinuous phases would thus be a function of geometry, that is independant of the average size of the particles, though a larger distribution of particle sizes makes for relatively less void space available to be filled by liquid. The same volume-to-volume ratio for a putty would be more or less independent of the chemical compositions of the two phases, though their weight-to-weight ratio would depend on their relative densities. A classic composition uses ca. 15% w/w (which corresponds to 34% v/v) of water-insoluble vegetable oil as continuous phase, with inorganic whiting (powdered calcium carbonate) as discontinuous phase; other compositions substitute Fuller's earth (clay) for the discontinuous phase. More modern compositions use low-molecular-weight polysulphides, silicones, or oligomeric hydrocarbons as the "oil" or "continuous" phase, and a wide variety of materials as "filler" or "discontinuous phase". Sometimes also the continuous phase consists of or includes monomer that can be cured to a rigid matrix after the desired shape has been formed.
The required qualities for a composition of matter that would be a buoyant putty to hold sinkable objects would be: lowest possible density for maximum buoyancy; malleability towards deliberate shaping by hand without the mass breaking or crumbling, yet sufficient stiffness that it does lose hold of a sinkable object through flow due to gravity or normal manipulation of the object; self-adhering and cohesive so that it does not crumble or break upon deliberate hand manipulation, and that it can be made to wrap around a sinkable object as a continuous ring or band and thus hold it against forces of gravitation or normal manipulation, yet not adhesive and not leaving either solid crumbs or liquid stains on hands and other surfaces; non-toxic towards handling or accidental ingestion; odourless and resistant to decay; inert and non-absorbant towards water; non-flammable and inert to air; not damaged by light, vibration or shock; retains essential mechanical properties within temperature of normal use, for example, -40.degree. C. to +40.degree. C.; long shelf and storage life without curing to a solid that cannot be shaped by hand, nor breaking down to a liquid that loses form due to mere gravity or normal manipulation of a held sinkable object; can be made brightly coloured, reflective, fluorescent or phosphorescent for easy location of held sinkable object on water surface; ease and low cost of production. Though able to function as a buoyant putty by itself, optionally such a composition of matter could also be enclosed in a flexible envelope which need not be impermeable to liquids, for example a woven or knitted fabric, that could also be fitted with ties or adhesives to better hold or contain a sinkable object.
The prior art has no examples that meet all these requirements together.
U.S. Pat. No. 5,459,959 to Daniel L. Paradis issued Oct. 24, 1995 describes a "Fish strike indicator composition" that is a moldable, buoyant composition comprising either unexpanded or expanded EXPANCEL.RTM. expandable thermoplastic microspheres dispersed in equal volumes of corn syrup or other sugar component, and hydrocarbon resin. While still in unexpanded form, the EXPANCEL.RTM. microspheres are mixed with the other components, then the entire composition is heated in a microwave oven to expand the microspheres to their final size and fill the package. This composition has the disadvantages of being sticky, subject to biodegradation, and detectably water-absorbing, which last the inventor suggests can be offset by adding hydrophobic silica--a relatively dense ingredient--in mass equal to the microspheres. This same patent also mentions "Strike Putty #835L", sold by ORVIS.RTM. Company of Manchester Vt. USA, a "clay like" material composed of glass microballoons and hydrocarbon resins, which has the disadvantages of relatively poor buoyancy (density 0.6 g/mL), and a tendency to absorb water on repeated or prolonged use.
U.S. Pat. 5,421,874 to Tony M. Pierce issued Jun. 06, 1995 describes a "composite microsphere and lubricant mixture" for use within flexible containers cushions and padding, in which the microspheres can be plastic and the lubricant can be silicone-based, possessing "a low specific gravity, low thermal mass, low coefficient of heat transfer, insulative and flotation qualities". This patent specifies that the lubricant must be a low-viscosity liquid, such as soapy water or other liquid of similar consistency, explicitely excluding more viscous "lubricants which impede rather than facilitate sliding and rolling movement of spherical objects with each other, such as stiff wax", so that the entire composite mixture has a "low shearing force threshold", being "quick to flow" that it may function as a cushioning material in a chair or bed without even temporarily-perceptible bumps, which would be a disadvantage for a buoyant putty that must be sufficiently stiff and strong to retain a sinkable object against gravity and normal manipulation of the object, and that thus requires a highly viscous liquid as the continuous phase. Again with the object of making the composition less stiff, this patent also specifies that the low-viscosity "lubricant means is present on the exterior surface of essentially all of said spherical objects, but in a quantity less than would cause dispersion of said spherical objects in said lubricant means", with a preferred embodiment of 1 g/mL liquids being mixed with plastic microspheres to give a "specific gravity for the composite mixture of about 0.2 to 0.25 or less", which composition would have the disadvantage in a buoyant putty of having a low cohesive strength for holding a sinkable object; mention of other embodiments with densities "above 0.50" clearly refers to compositions with denser continuous, for example, fluorocarbon, or discontinous, for example, solid or thicker-walled glass, ceramic or metal microspheres phases, rather than higher volume-to-volume ratio of continuous-to-discontinuous phases. This prior art would also have the disadvantage of the composition having to be confined in a liquid-impermeable flexible bladder or flexible container, to keep the mass from flowing or breaking apart due to low shearing force threshold and low cohesive strength respectively, and to block the exudation of its low-viscosity liquid.
Other U.S. Pat. Nos. namely, 5,362,543 to Lincoln P. Nickerson issued Nov. 08, 1994, 4,728,551 to Eric C. Jay issued Mar. 01, 1988, and 4,255,202 to Jack C. Swan issued Mar. 10, 1981, all describe "flowable pressure compensating fitting materials which are used in seating applications". Here the continuous phase is a low-viscosity oil or a more viscous mixture of oil with wax, fatty amide or denser colloidal silica that form a fine suspension in the oil, and the discontinuous phase consists of hollow glass or plastic microbeads to reduce overall density to some extent. In particular, the Nickerson patent teaches a continuous phase made of an oil that is a poly(dimethylsiloxane) of viscosity below 100 cstks, together with at least 3 wt % of a fatty amide thickener that is insoluble in the oil. All these materials have the disadvantage that the low-molecular weight oil is able to seep past the suspended wax microcrystals or fatty amide particles or colloidal silica that are meant to increase its apparent bulk viscosity, as well as past the microspheres, so as to collect at the surface of a portion of the material, thus requiring a liquid-impermeable flexible envelope to contain such exudation, and tending to exhibit phase-separation even within such envelope. For similar reasons, these materials also have the disadvantage of low cohesive strength for a buoyant putty holding a sinkable object.
U.S. Pat. No. 5,202,362 to Jules J. Hermale issued Apr. 13, 1993 describes a composite of silicone fluid and thermoplastic microspheres, but the silicone fluid is again of low viscosity (20,000 centistokes=20K cstks) that would mean low cohesive strength and exudation, and moreover contains reactive groups so that it can be cured to a solid mass upon injection into the ear, which would be disadvantageous for a moldable buoyant putty. Prior art U.S. Pat. Nos. 4,000,108 to Yokokawa et al issued Dec. 28, 1976 and 4,861,804 to Nakanishi issued Aug. 29, 1989 for polysiloxane-microsphere composites also employ polysiloxanes that are curable so as to crosslink to non-flowing gels with the same disadvantage.